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Thread: Color sanding

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    Default Color sanding

    For the bicycle painters out there, does anyone prefer to color sand after the final clear coat, then buff and use a hand glaze. Or do you guys recommend wet sanding prior to the final clear coat?

    Thanks!

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    Default Re: Color sanding

    Hi Jeff,

    For me, the short answer is that "it depends". I nearly always sand before the final clear coat. I sometimes "cut and buff" after the final clear, but generally only to remove an isolated dust nib or etc. Cutting and buffing an entire bike frame, especially a lugged one, with all of their nooks and crannies isn't very appealing to me.

    Dave
    Dave Anderson
    Anderson Custom Bicycles
    www.andersoncustombicycles.com
    ACB on Facebook
    ACB on flickr

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    Default Re: Color sanding

    Jeff,

    Color sanding usually refers to small touch up sanding directly on your basecoat, before any clear is applied. If I'm interpreting your query correctly, you are asking if after the final clear, painters are sanding down the finish and buffing it back out with a compound.

    I prefer to level my layers before the final clear by sanding and then shooting a very hot (heavily reduced) final clear that will burn into the previous layers and smooth everything out like glass. Shooting a heavily reduced final coat can be incredibly frustrating though, as if you are not practiced, you'll have runs all over the place. The trick to this is building a paint fixture that allows you to continually rotate the frame, keeping it moving, so you use gravity to your advantage, avoiding sags or runs as the catalyst hardens the final coat.

    Much like Dave, I will getly touch up a small dust nib with a quick hit of 1200 grit and a little Perfect-It if necessary.

    I never, ever, polish out an entire frame...way to time consuming. I prefer to adopt a process that makes it unnessary.

    If you have the inclination and time, buried in my blog are numerous posts detailing the paint process.

    Good luck,

    rody

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    Default Re: Color sanding

    Jeff, I do a final sand before a very reduced final clear.

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    Default Re: Color sanding

    Thanks for the advice. I painted 2 frames last week (my 3rd and 4th try) and was unhappy with the final finish. I had a bit of orange peel and dry spray so I ended wet sanding with 1500 grit and hand rubbed the finish with Meguiar's #2 fine-cut cleaner.

    Dave and Rody- You guys are 100% right, I finished about 10 hours later. I was thrilled with the finished product, however, no way to make a profit with that method.

    Again, thanks for the help!

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    Default Re: Color sanding

    Jeff,

    Post up some pics of the finish before sanding and a quick detail of the product you are using, gun and setting parameters. We'll see if we can't help you tweak it a bit to save you some time.

    r

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    Default Re: Color sanding

    Rody,

    Here's a picture of the worst part of the frame. I was using PPG's Shop-line epoxy primer (JP375) mixed 2:1:.5, urethane basecoat (JBPC) mixed 1:1 with JR506 reducer and MC262 clear mixed 4:1 with the hardener (MH267). I sprayed the primer on Monday, main and secondary color Wednesday, applied decals and sprayed 3 coats of clear on Thursday. I use a a Sata 3000 B RP with a 1.3mm tip between 25-27 psi for everything. What do you think? photo (4).JPG

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    Default Re: Color sanding

    Jeff,

    Just finishing for the day and gonna go ride, so here are some quick, random thoughts...

    The products you are using look fine (reducer in right range, all compatible, etc...).

    Based on your location, unless you are spraying in a climate controlled booth, you probably have had some warm, humid conditions. They can be tough to get your mixtures right as the standard recommended ratios always need tweaked a bit.

    Looking at your timeline, one thing you will want to keep in mind for durability is the paints ability to adhere to the layers beneath. Most PPG products have a maximum of 24 hours to get your next coat down...there is no need to wait that long though. In fact, once the coats flash off, you should be good to move on. This will help in adhesion as well as allow the layers to burn into each other, smoothing everything out.

    A good base starts with thin primer layers. I throw out the reducer ratio and really allow the climate to tell me where it needs to be. I add reducer until a stainless spoon dipped into the mixture and lifted out has just a thin, almost transleusant layer. Multiple coats with a quick sand for dust nibs between will set you up with a smooth surface for your base layers. Blow off with filtered air and tack cloth before moving on.

    For your bases and clears, you are definately getting too much atomization resulting in dry spray. Many factors contibute; you are using a fairly large tip size for small tubing, requiring you to increase your air ratio. I generally run a .8 to 1.0 tip depending on the material being sprayed. Regardless, the majority of your issue may be application. Work on a technique that allows you to move around the bike systematically, gun perpendicular to the tube surface, while avoiding overspray onto existing coats. Keep an even spacing between the gun and frame and consistant movement. Hook up all your equipment and a bare frame and just shoot air, practicing moving around the frame and developing a pattern, it really helps. Then throw in some gun cleaner and just shoot that, practicing watching the material lay on the tube, varying your speed and distance til you achieve an even spray pattern on the tube. This more than any mixing ratio will help your finishes progress.

    I'd recommend laying down one layer of clear before applying decals. This way if you do make an application mistake, it is less likely to damage the base layers, which are difficult to correct.

    Before your final clear coat, systematically sand it down with 800-1000 grit, blow off with filtered air, and tack cloth. Mix your final clear with a bit more reducer and move quickly and efficiently. If you have the ability to rotate or move the frame to prevent sags, it will help tons.

    That's all for now, my daughter wants to hit the trail :)

    rody

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    Default Re: Color sanding

    Rody,

    Thanks for the advice. It appears practice, consistent (correct) technique, and persistence will pay off. I was telling Jonathan how much I enjoy the process. After 12 framesets and 4 paint jobs, its slow going but I'm happy with the results. I feel like I have a repeatable process for building, now painting is a complete new challenge. I appreciate the help.

    Jeff

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    Default Re: Color sanding

    I'm glad Jeff asked this question because I found allot that will help me as well. For clarification, what is meant by "heavely reduced"? My clear suggests 5-10%. Would that mean 15%?
    Cheers
    Kevin

    PolyTube Cycles

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    Default Re: Color sanding

    Kevin,

    so much matters on the atmospheric variables and just how far into the acceptable temperature range you are pushing your reducer, or how quickly your reducer will be flasing off.

    I'll be honest, I abandoned ratios long ago and do so much by feel/look now it makes it hard to convey in written text. I normally look for a consistency that allows the final clear to run freely off a spoon, with a nice even sheen left behind. Thicker than water, kinda like REAL maple syrup...thin and fast and full of goodness, maybe 20%-25% more reducer. It will force you to move quickly and be efficient...overlaps of areas or lingering too long will result in drips/runs on the tubes.

    Success will be in a crystal clear that is smooth, even, and laughs at the thought of needing to polish it out.

    maltese cross small.jpg

    I've been meaning to post a video on paint, perhaps I'll have to work on one during the next finish.

    good luck,

    rody

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    Default Re: Color sanding

    I sort of do what Rody does. For Imron color and clear I mix 3:1:1 and then an extra splash or so of reducer depending on temp. It can be mid 90's here. The guys at the paint shop say reducer is not even needed, well maybe on a dump truck it's not. With ppg DBC and HoK I follow the published ratios for the color coats, but the clears get an extra splash or so, again depending on temp and which clear, first or last. Btw, I've been locking down my dbc color coats with 5% dx59 and I like how it all goes together much better. I'm always interested in how others do it because I don't think anyone is the same.

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    Default Re: Color sanding

    Thanks! sounds like I've been going too thick (usually well under 10 %). I'll try the spoon test.
    Cheers
    Kevin

    PolyTube Cycles

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    Default Re: Color sanding

    Almost midnight here and I just finished trying the above. I have never been able to get a clear as smooth as I did this time. Big thanks for the tips!
    Cheers
    Kevin

    PolyTube Cycles

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    Default Re: Color sanding

    Sweet Kevin...pics are required for 100% reader satisfaction

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    Default Re: Color sanding

    OK here you go:
    A De Rosa Avant. I had to flatten out the clear because it was too shiny compared to the original:


    After polishing the transition away (it's actually not visible in real life but you can still see it here):



    A Stock aero that still needs to be de-masked:




    One thing I noticed is that the clear shows imperfection on the surface more. That's something I'll need to work on during prep.
    Last edited by datas_brother; 06-24-2013 at 07:03 AM. Reason: pick the richt word.
    Cheers
    Kevin

    PolyTube Cycles

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    Default Re: Color sanding

    Kevin,

    Yep, when it gets that thin and hot, it does not hide imperfections as well. Keep her tight!

    r

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